JP2011235242A - Method for manufacturing granulated improved soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing epoch-making granulated improved soil excelling in practicability and safely usable with a sense of security without soil contamination while suppressing the elution of a noxious chemical substance into soil to a soil environmental standard value or lower even if using construction sludge and waste gypsum boards heretofore dumped in a final disposal site.SOLUTION: The method for manufacturing granulated improved soil for recycling construction sludge discharged from a construction site or the like into granulated improved soil includes mixing waste gypsum board powder obtained by crushing waste gypsum boards, into the construction sludge at 50% or less to the weight of the construction sludge to obtain a primary mixture, mixing cement into the primary mixture at 20% or less to the weight of the primary mixture to obtain a secondary mixture, and kneading, drying and solidifying the secondary mixture to manufacture the granulated improved soil.

Description

  The present invention reuses construction sludge and waste gypsum board that have been disposed of as final industrial waste, and reuses them as construction materials such as roadbed materials, backfill materials, slope curing, and herbicide materials. The present invention relates to a method for producing a modified granulated material.

  Conventionally, construction sludge generated in connection with construction sites or road construction has been dewatered and then landfilled as industrial waste at a managed final disposal site. However, in recent years, the remaining capacity of the final disposal site for industrial waste has become tight, and it is said that the remaining number of years is another few years, and it is urgent to consider the reduction and reuse of industrial waste. It has become a challenge.

  Even in such a situation, the recycling rate of construction sludge is currently at a very low level. For example, a granulated improved soil that reuses various construction sludges such as Patent Document 1 has been proposed. Not yet commercialized.

  In addition, as with construction sludge, there is an urgent need to consider recycling of waste gypsum boards that are generated in large quantities as waste materials at new construction sites and demolition sites.

  This waste gypsum board has been separated from paper and gypsum board and processed at the stable final disposal site. However, after 2006, it can no longer be processed at the stable final disposal site. Landfill processing is performed at the disposal site, and as with the construction sludge described above, this is one of the factors that are constraining the remaining capacity of the final disposal site.

  With regard to the waste gypsum board, most of the waste gypsum board that is generated at production sites and new construction sites has been established. Reuse is not progressing, and the rate of reuse is only about a few percent of the total emissions. Therefore, the overall recycling rate of waste gypsum board is around 20% in terms of the ratio of emissions. At present, the ratio is very low.

JP 2008-036532 A

  If the above-mentioned construction sludge and waste gypsum board are reused to make granulated improved soil for construction materials, the chemical substances eluted from this granulated improved soil may exceed the soil environmental standard value and cause soil contamination. This has been regarded as a problem, and in the conventionally proposed granulated improved soil, this soil contamination has not been taken into consideration, and this has been one of the causes that has not been put into practical use.

  Specifically, conventionally, when construction sludge is reused as granulated improved soil, cement is used as a solidifying material to solidify the construction sludge. This cement contains hexavalent chromium. Usually, when used in concrete, it is taken into the cement hydrate and does not elute into the soil, but when mixed with granulated soil, the hydration reaction between this hexavalent chromium and cement In such a state, if it is backfilled in the soil, hexavalent chromium may be eluted from the granulated improved soil and contaminate the soil or groundwater.

  In some cases, gypsum is used as the solidifying material, but when this gypsum is mixed, fluorine contained in the gypsum is eluted and contaminates the soil.

  Furthermore, when reusing waste gypsum board powder obtained by crushing waste gypsum board as this gypsum, the organic components such as paper contained in this waste gypsum boat powder are subject to the metabolism of sulfate-reducing bacteria inhabiting groundwater. There is also the possibility of generating hydrogen sulfide.

  Thus, even if it is recycled as granulated improved soil using construction sludge and waste gypsum board, it has not been put into practical use because of the high possibility of soil contamination.

  Therefore, the present invention is an epoch-making granulation improvement excellent in practicality that can suppress the elution of harmful chemical substances into the soil below the soil environmental standard value and can be used safely and safely without soil contamination. It aims at providing the manufacturing method of soil.

  The gist of the present invention will be described with reference to the accompanying drawings.

  A method for producing granulated improved soil that recycles construction sludge discharged from construction sites, road construction sites, etc. into granulated improved soil, and waste gypsum obtained by pulverizing waste gypsum board into the construction sludge Board powder is mixed at a ratio of 50% or less with respect to the weight of the construction sludge to obtain a primary mixture, and cement is mixed with the primary mixture at a ratio of 20% or less with respect to the weight of the primary mixture to obtain a secondary mixture. The present invention relates to a method for producing a granulated improved soil, characterized in that a mixture is obtained, the secondary mixture is kneaded, dried and solidified.

  Further, the construction sludge is a dehydrated cake that has been dehydrated to a water content of 40% or less, and relates to the method for producing granulated improved soil according to claim 1.

  The mixing ratio of the waste gypsum board powder is 30% to 40% with respect to the weight of the construction sludge, The granulated improved soil according to any one of claims 1 and 2, It relates to a manufacturing method.

  The method for producing a granulated improved soil according to any one of claims 1 to 3, wherein the mixing ratio of the cement is 7% to 15% with respect to the weight of the primary mixture. It is concerned.

  Moreover, the paper component contained in the said waste gypsum board powder shall be 4% or less with respect to the weight of this waste gypsum board powder, The granulation improvement of any one of Claims 1-4 characterized by the above-mentioned. It relates to a method for producing soil.

  Moreover, the said cement is blast furnace cement, It concerns on the manufacturing method of the granulation improvement soil of any one of Claims 1-5 characterized by the above-mentioned.

  Since the present invention is as described above, when used for roadbed materials, backfill materials, slope curing, herbicide materials, etc., it becomes an excellent granulated improved soil having strength that does not re-mud, and in the soil This makes it possible to control the amount of elution of fluorine and hexavalent chromium to below the soil environmental standard value, and to produce a granulated improved soil that can be used safely and safely without generation of hydrogen sulfide.

  In addition, by reusing construction sludge and waste gypsum board that were previously disposed of in a managed final disposal site, the amount of industrial waste discharged can be reduced, and the load on the final disposal site can be reduced. This leads to the prolongation of the remaining years of the final disposal site, and furthermore, as mentioned above, it can be used as a roadbed material and backfill material, so conventionally, mountain sand has been used for this purpose. It will be an environmentally friendly and innovative method for producing improved granulated soil that will contribute to the prevention of destruction of the natural environment by collecting mountain sand.

  Further, in the inventions of claims 2 and 3, by controlling the moisture content of the construction sludge to 40% or less, the mixing amount of the waste gypsum board as a humidity control material is a predetermined amount or less, specifically, the construction sludge Since it can be 30% to 40% by weight ratio, even when backfilled into the soil as granulated improved soil, the amount of fluorine elution is kept below the soil environmental standard value, and there is no concern about soil contamination. It becomes the manufacturing method of granulation improvement soil.

  Further, in the invention according to claim 4, since the elution amount of hexavalent chromium is suppressed to a soil environmental standard value or less, there is no concern about soil contamination, and the strength as a construction material has sufficient strength. It becomes a method for producing a granulated improved soil that is excellent in safety and practicality.

  In the invention according to claim 5, it is a method for producing a granulated improved soil excellent in safety without worrying about generation of hydrogen sulfide.

  Moreover, in the invention of claim 6, for example, since the content of hexavalent chromium is less than that of Portland cement, it is excellent in safety, and excellent in practicality that exhibits excellent performance even in long-term strength. It becomes the manufacturing method of granulation improvement soil.

It is a soil test result list of a present Example.

  The preferred embodiment of the present invention will be briefly described by showing the operation of the present invention.

  In the present invention, the proportion of gypsum board powder obtained by pulverizing waste gypsum board mixed as a humidity control material in construction sludge was reduced to 50% or less. The amount of fluorine eluting into the soil can be reduced to a soil environment standard value or less (specifically 0.8 mg / l or less), and this is a safe method for producing improved granulated soil without worrying about soil contamination.

  In addition, by mixing this humidity conditioning material, the amount of cement mixed as a solidifying material is reduced to a small amount (specifically, 20% or less based on the weight of the primary mixture in which gypsum powder is mixed into construction sludge). Since it can be made into a granulated improved soil that does not re-sludge, the manufacturing cost can be reduced, and the amount of hexavalent chromium contained in the cement is less than the soil environmental standard value. (Specifically, 0.05 mg / l or less), which is a method for producing a granulated improved soil excellent in economy and safety.

  In addition, since the present invention recycles construction sludge and waste gypsum board, which have been discharged as industrial waste, as construction materials, it is possible to extend the life of the final treatment plant for industrial waste that has a short remaining capacity. Furthermore, by using this granulated improved soil for construction materials such as roadbed materials and backfill materials, it is not necessary to use the mountain sand that has been obtained by shaving the mountains. Therefore, it becomes an innovative method for producing improved granulated soil that plays an important role in preventing natural destruction and forming an environmentally friendly recycling society.

  Also, for example, before mixing gypsum board powder into construction sludge, dehydration can be performed to make a dehydrated cake with a moisture content of 40% or less, and then gypsum board powder is mixed, thereby reducing the mixing ratio of this gypsum board powder. Thus, the amount of fluorine elution can be reduced, and a safer and more environmentally friendly method for producing granulated improved soil is obtained.

  Specific examples of the present invention will be described.

  The present embodiment is a method for producing granulated improved soil that recycles construction sludge discharged from construction sites, road construction sites, etc. into granulated improved soil, and pulverizes waste gypsum board into the construction sludge. The waste gypsum board powder obtained in this way was mixed at a ratio of 50% or less with respect to the weight of the construction sludge to obtain a primary mixture, and cement was added to the primary mixture at a ratio of 20% or less with respect to the weight of the primary mixture. This is a method for producing a granulated improved soil in which a secondary mixture is obtained by mixing, the secondary mixture is kneaded, dried and solidified.

  Construction sludge (inorganic sludge) discharged from construction sites and road construction sites can be broadly divided into two types of construction sludge: mud and dewatered sludge. In the case of dewatered sludge, that is, sludge with a low water content, Although most of the construction sludge is the former, the moisture content of this construction sludge is high, so it will not solidify properly if the ratio of humidity control material and solidification material is not increased. The predetermined strength is not reached, and the performance as the granulated improved soil is not exhibited (re-mud).

  Therefore, in the case of construction sludge with a high water content such as mud, after coagulation / sedimentation and pH adjustment, check the dehydration state using a water content measuring device such as an infrared moisture meter (confirm the water content). While performing dehydration treatment (for example, filter press dehydration treatment) to obtain a dehydrated cake adjusted to a predetermined moisture content.

  This dehydration process can squeeze out the moisture contained in the construction sludge as long as the time is extended, so that a dehydrated cake with a low moisture content can be obtained. However, on the other hand, by prolonging the processing time, there arises a problem that the processing capacity (working efficiency) is lowered and the cost is increased.

  Therefore, in this example, the time for this dehydration treatment is optimized, and the moisture content of the obtained dehydrated cake is adjusted to be 30% to 40%.

  The dehydrated cake adjusted to a moisture content of 30% to 40% is mixed with a humidity adjusting material at a ratio of 50% or less with respect to the weight of the dehydrated cake to obtain a primary mixture.

  This humidity control material uses waste gypsum board powder that is generated in large quantities as waste material at new construction sites and demolition sites. Specifically, this waste gypsum board powder is made of waste gypsum board. The waste gypsum board that has been crushed by the crushing machine is put on a separation device, the waste gypsum board and the paper component are separated, and the waste gypsum board from which the paper component has been separated is further processed by a particle size sorting device. Powdered waste gypsum board powder.

  In addition, as described above, the waste gypsum board powder excludes most of the paper components by the separation device, but 100% of the paper components cannot be excluded, and this paper component (organic component) is included. When the granulated improved soil is backfilled in the soil, this paper component becomes a factor that generates hydrogen sulfide due to the metabolism of sulfate-reducing bacteria inhabiting the groundwater. Therefore, if there are many paper components contained in waste gypsum board powder, there will be more paper components (organic components) contained in the granulated improved soil, and there is a higher risk of generating hydrogen sulfide when backfilled in the soil. There are concerns about environmental problems and effects on the human body.

  Generally, if the paper component contained in this waste gypsum board powder contains 5% or more of the weight of the waste gypsum board powder, it is said that there is a risk of generating hydrogen sulfide. In this example, the paper component, that is, the organic component contained in the waste gypsum board powder is removed by the above-described separation device, and the waste gypsum board powder is processed so as to be 4% or less based on the weight of the waste gypsum board powder. Therefore, even if the granulated improved soil produced by the production method in the present embodiment is backfilled in the soil, hydrogen sulfide is not generated and can be used with confidence.

  Further, the amount of waste gypsum board powder mixed in the dewatered cake is determined by the weight of the construction sludge as described above, but the ratio varies depending on the amount of water contained in the construction sludge.

  That is, for example, when waste gypsum board powder is mixed in the same amount of construction sludge having a moisture content of 40% and construction sludge having a moisture content of 50%, for example, in a proportion appropriate to construction sludge having a moisture content of 40%. In the obtained primary mixture, construction sludge with a moisture content of 40% becomes a primary mixture adjusted to a desired moisture content, but construction sludge with a moisture content of 50% becomes a primary mixture that is damp and lacks humidity control materials. End up. Therefore, the primary mixture obtained from construction sludge with a moisture content of 50% will solidify properly unless the amount of solidified material to be mixed in is greater than the primary mixture obtained with construction sludge with a moisture content of 40%. There is a possibility of re-mudging.

  Therefore, if the water content of the primary mixture is not constant, the ratio of mixing with the solidified material must be adjusted each time, which takes time, reduces work efficiency, and increases costs.

  Therefore, in this example, when the moisture content of the construction sludge is low, the proportion of waste gypsum board powder mixed is reduced, and when the moisture content is high, the proportion of waste gypsum board powder mixed is increased, and the soil quality of the primary mixture is increased. The state is adjusted to be substantially constant, and the amount of solidified material mixed thereafter is set to a constant amount so that the processing can be performed.

  In addition, this waste gypsum board powder contains fluorine. If the proportion of this waste gypsum board powder increases, the amount of fluorine contained in the granulation improved soil also increases. For example, this granulation improvement When the soil is backfilled in the soil, the amount of fluorine eluted from the granulated improved soil increases, and fluorine above the soil environmental standard value (0.8 mg / l or more) may be eluted in the soil.

  Therefore, as described above, if the proportion of waste gypsum board powder used as a humidity control material is small, the moisture content in the construction sludge is high and difficult to solidify. As a result, there is a problem that the manufacturing cost increases, and if there is a large proportion of waste gypsum board powder mixed in, the amount of fluorine elution will exceed the soil environmental standard value and cause soil contamination. Occurs.

  Therefore, in this example, the moisture content of the dehydrated cake after the dehydration treatment is managed to be in the range of 30% to 40%, and the ratio of mixing the waste gypsum board powder is further included in the moisture content of the dehydrated cake. In addition, the above-mentioned problems are solved by mixing at an optimal ratio as appropriate, and the manufacturing method of the granulated improved soil is low-cost and environmentally friendly.

  Moreover, in this example, the ratio of mixing the waste gypsum board powder was set such that the highest priority was given to no soil contamination, that is, no elution of fluorine above the soil management reference value. Therefore, the elution test of fluorine with respect to the mixing ratio of waste gypsum board powder was conducted, and the optimal mixing ratio of waste gypsum board powder was set.

  As shown in Table 1, the results of the elution test for fluorine confirmed that the elution amount of fluorine was below the soil environmental standard value (0.8 mg / l or less) even at a mixing rate of 50%. It was confirmed that the fluorine elution amount was 0.21 mg / l even with only the dehydrated cake not mixed with board powder. In other words, the construction sludge itself discharged from the construction site or road construction site already contains fluorine.

  Therefore, although it was confirmed from the test results that the elution amount was below the soil environmental standard value up to a contamination rate of 50%, the waste gypsum of this example was considered in consideration of the variation in fluorine content in construction sludge and safety. The board powder mixing rate was set to 40% or less with respect to the weight of the dehydrated cake.

  More specifically, since the moisture content of the construction sludge after dehydration is controlled to be 30% to 40%, the amount of waste gypsum board powder mixed is determined each time depending on the moisture content of the construction sludge. For example, when the moisture content of construction sludge is 30%, the mixing rate of waste gypsum board powder is set to 30%, and when the moisture content of construction sludge is 40%, the mixing rate of waste gypsum board powder is set to 40%. Set to%.

  In this way, waste gypsum board powder was mixed in a dehydrated cake with a water content of 30% to 40% obtained by dehydrating construction sludge in a proportion of 30% to 40% with respect to the weight of the dehydrated cake. A mixture is obtained, and cement as a solidifying material is mixed into the primary mixture to obtain a secondary mixture.

  This cement is for solidifying to a strength that does not cause re-mudging even when the granulated improved soil absorbs moisture when it is made into granulated improved soil.

  In addition, the cement used in this solidifying material contains hexavalent chromium, and if this hexavalent chromium is eluted in large amounts in the soil, it may contaminate the soil and groundwater, causing environmental problems. . Therefore, the elution amount of hexavalent chromium must be suppressed to a soil environment standard value of 0.05 mg / l or less, and in order to reduce the elution amount of hexavalent chromium, the mixing ratio of cement as a solidifying material It is important to keep the amount as small as possible.

  Also, in this example, blast furnace cement is adopted as this cement, and this blast furnace cement has less hexavalent chromium content than general Portland cement, and further has excellent performance in long-term strength. Therefore, it is very suitable for use in granulated improved soil.

  In this example, considering the elution amount of hexavalent chromium described above, and as a condition for preventing re-mudging when the granulated improved soil is used, the mixing ratio of this blast furnace cement is based on the weight of the primary mixture. It is obtained from experiments that it should be 7% or more. However, since the water content in the primary mixture varies to some extent, the final blast furnace cement mixing ratio is 10% with respect to the weight of the primary mixture in consideration of the safety factor.

  Moreover, the elution amount of hexavalent chromium when blast furnace cement is mixed at a rate of 10% with respect to this primary mixture is 0.02 mg / l or less, sufficiently clearing the soil environment standard value of 0.05 mg / l. To get results.

  The secondary mixture thus obtained is kneaded and granulated by a kneading granulator, and the granulated and improved granulated soil is cured for about 4 weeks to improve the strength.

  In this example, a soil test was conducted on the soil properties of the granulated improved soil produced by the method for producing the granulated improved soil described above, and it was confirmed that the soil was effective as the granulated improved soil.

  In addition, the granulated improved soil used in the soil test was mixed with waste gypsum board powder in a proportion of 30% of the weight of the dehydrated cake in a dehydrated cake with a moisture content of 30%, and the weight of this primary mixture It was obtained by mixing blast furnace cement at a rate of 10%.

  The results of soil tests are shown below (see Fig. 1 for a list of test results).

In the soil particle density test, the samples were placed in three containers and measured with different pycnometers. As a result, the soil particle density was 2.654 g / cm ^{3 to} 2.669 g / cm ³ , and the average density was It was 2.663 g / cm ³ .

  In the soil moisture content test, samples were placed in three containers, and the moisture content was calculated from the mass difference before and after oven drying. As a result, the average moisture content was 21.7% to 22.8%. The result was 4%, and the natural moisture content was not so high.

  In the soil particle size test, the sand content (particle size: 0.075 mm to 2 mm) is 27% and the silt content (particle size: 0. 005 mm to 0.075 mm) and clay (particle size less than 0.005 mm) were 73%, and the maximum particle size was 2 mm.

  Further, in the consistency (soil liquid limit / plastic limit test), all results were NP (Non Plastic), and a result of not re-mudging even when moisture was added was obtained.

Moreover, in the soil compaction test (consolidation characteristics) by tamping, the test method is Bc, that is, the type of tamping method is B (rammer mass 2.5 kg, mold inner diameter 15 cm, number of tamped layers). 3 layers, tamping frequency 55 times / layer, allowable maximum particle size 37.5 mm), c (wet method, non-repetitive method) was used as a sample preparation method and usage method. As a result, the maximum dry density was 1.095 g / cm ³ and the optimum water content ratio was 46.9%.

  Moreover, in the CBR test, the test method is performed with compacted soil, the expansion ratio is 0.38%, the moisture content after the penetration test is 54.0%, and the average CBR value is 37.2%. In addition, in the CBR test, a high numerical value was obtained, the foundation ground support force was sufficient, and a result that could be used sufficiently for soft ground countermeasures was obtained.

  Further, in the pH test of the soil suspension, the pH value was 10.0, which was slightly alkaline. This is probably because cement is used as the solidifying material.

  In addition, in the result of the cone index test, the penetration was impossible, the trafficability was good, and the workability was good in the embankment work.

  Thus, from the result of the above soil test, the granulated improved soil produced by the production method shown in the present example is a soil with a lot of fine-grained soil, but adhesive strength can also be expected by the blast furnace cement which is a solidifying material. Since it has properties and sufficient strength can be obtained after compaction, it was confirmed that it could be used without problems as a granulated improved soil for construction materials.

  In other words, when used as a backing material or backfill material for civil engineering structures, etc., the compressibility (deformation) is generally small, the workability to obtain the required strength, the filling property and stability around the buried object, etc. However, the improved granulated soil produced by the method for producing improved granulated soil shown in this example has a fine particle size, can be sufficiently filled in the gaps in the structure, has low compressibility, and has no problem with its bearing capacity. Moreover, it does not contain any chemical substances that have an adverse effect on the surroundings of the buried object, and further, it is a granulated improved soil that has a large amount of fine particles and does not damage the structure and is easy to work.

  The present invention is not limited to the present embodiment, and the specific configuration of each component can be designed as appropriate.

Claims (6)

  A method for producing granulated improved soil that recycles construction sludge discharged from construction sites, road construction sites, etc. into granulated improved soil, and waste gypsum obtained by pulverizing waste gypsum board into the construction sludge Board powder is mixed at a ratio of 50% or less with respect to the weight of the construction sludge to obtain a primary mixture, and cement is mixed with the primary mixture at a ratio of 20% or less with respect to the weight of the primary mixture to obtain a secondary mixture. A method for producing a granulated improved soil, characterized in that a mixture is obtained, the secondary mixture is kneaded, dried and solidified.   The method for producing granulated improved soil according to claim 1, wherein the construction sludge is a dehydrated cake that has been dehydrated to a water content of 40% or less.   The method for producing granulated improved soil according to any one of claims 1 and 2, wherein the mixing ratio of the waste gypsum board powder is 30% to 40% with respect to the weight of the construction sludge. .   The method for producing granulated improved soil according to any one of claims 1 to 3, wherein a mixing ratio of the cement is 7% to 15% with respect to a weight of the primary mixture.   The paper component contained in the waste gypsum board powder is 4% or less based on the weight of the waste gypsum board powder. The granulated improved soil according to any one of claims 1 to 4, Production method.   The method for producing granulated improved soil according to any one of claims 1 to 5, wherein the cement is blast furnace cement.

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